The invention relates to a leg prosthesis with an artificial knee joint according to the preamble of claim 1 and a method for controlling a leg prosthesis according to the preamble of claim 14.
When walking with a prosthesis, the prosthesis upper leg is moved by the leg stump in a forward direction during the walking. If the damping is not adapted, due to its inertia, the lower leg may be angled to a very large extent. The person wearing the prosthesis then has to wait until the prosthesis has moved back to its forward position before being able to place its foot on the ground. This results in unharmonic gait appearance, inappropriate timing performance and thus poor or less than optimal support properties.
There are known leg prostheses with an artificial knee joint where a damping element in the form of a pneumatic or hydraulic cylinder is provided for swing phase control and as a so-called fall back brake. The adaptation of the leg prosthesis to the person carrying it is achieved using a stationary gait analysis system. To this end, the person wearing the prosthesis has to perform a test walk with the prosthesis, e.g. on a running machine, with an orthopedic technician then providing a subjective judgement of the gait appearance. Together with the subjective feelings of the person wearing the prosthesis, the various components of the prosthesis are then adapted and set. Very often, the result of the setting is inaccurate, since the setting is carried out using subjective criteria. In addition, supplementary modifications such as weight, temperatures or the nature of the ground are not taken into consideration.
Further, the known damping elements for artificial knee joints have the drawback of not being able to respond fast enough to an abrupt change of the gait dynamics.
GB 1,191,633 discloses a leg prosthesis having an artificial knee joint with a hydraulically controlled brake, where a ferro-colloidal liquid or another magnetic liquid are used as the hydraulic liquid.
DE 195 21 464 A1 discloses a leg prosthesis having an artificial knee joint according to the preamble of claim 1 and a method for controlling such prosthesis according to the preamble of claim 14. In this leg prosthesis, when the type of gait is changed, the control of the knee brake can also be changed using a respective adaptation of a stored reference pattern. To various types of gait such as walking on flat ground or climbing stairs is associated a special control program, respectively, for controlling the knee brake. During the walking, the type of gait is determined by measuring the hip joint muscular activity and comparing the measured values with stored reference values, and the knee brake is controlled with the control program associated to this type of gait. The reference values for a type of gait are determined beforehand for each person wearing the prosthesis. However, there is no change of a control program associated to a specific type of gait.
In the known leg prosthesis, however, there is the problem that an adaptation of the prosthesis control, i.e. of the control programs, to changing circumstances with respect to the person wearing the prosthesis, such as gain or loss of weight of the person wearing the prosthesis or wearing different shoes, or with respect to the surroundings such as walking on flat ground on a bumpy path, is not carried out.
It is an object of the invention to provide a leg prosthesis having an artificial knee joint and a method for controlling such prosthesis, guaranteeing an optimum operation of the prosthesis and adapted to the person wearing it irrespective of changing operational circumstances as well as a fast reaction to abrupt changes in gait dynamics.
This object is achieved by a leg prosthesis according to claim 1 and by a method according to claim 14 for controlling such prosthesis. Further embodiments of the invention are presented in the dependent claims.